TL;DR
Carbon monoxide is odorless, colorless, and lethal. You cannot detect it without a detector. It's produced by every combustion source: generators, wood fires, gas stoves, camp stoves, car engines, propane heaters. Power outages create the highest risk because people bring combustion sources indoors. A CO detector on every floor is not optional.
The CDC reports that CO poisoning kills approximately 400 Americans and sends 50,000 to emergency rooms annually — with a spike every time a major storm or cold snap triggers power outages and people resort to emergency combustion heat sources. Most of these deaths are preventable with a working CO detector and knowledge of what not to run indoors.
CO Sources in Emergency Scenarios
The highest-risk scenario for CO poisoning is a power outage when people move combustion sources inside.
| Source | CO Production | Risk Level | |--------|--------------|------------| | Gas generator (5,000W) | Equivalent to ~100+ idling cars | EXTREME — never indoors or in attached garage | | Charcoal grill indoors | Very high | EXTREME — kills quickly in enclosed spaces | | Propane heater (unvented) | High | HIGH — requires specific ventilation or outdoor use | | Camp stove (propane/butane) | Moderate-high | HIGH — not for indoor use, even briefly | | Wood fireplace (open, chimney clear) | Low (exits via flue) | LOW when properly vented | | Wood stove (properly installed) | Low (exits via flue) | LOW when properly vented | | Gas kitchen range (burners) | Low per use | LOW — brief cooking with ventilation is normal use | | Vehicle idling in garage | Very high | EXTREME — even with garage door open | | Kerosene heater (unvented) | High | HIGH — requires significant ventilation |
The pattern: any combustion source in a space without deliberate, verified ventilation for that combustion volume is a CO hazard.
Symptoms by Exposure Level
CO replaces oxygen on hemoglobin — the symptoms mirror oxygen deprivation and worsen over time with continued exposure.
| CO Concentration | Symptoms | Time to Effect | |-----------------|---------|----------------| | 35 ppm | Headache after 6-8 hours | Threshold action level (OSHA workplace limit) | | 100 ppm | Headache within 2-3 hours | | | 200 ppm | Headache, dizziness, fatigue | 2-3 hours | | 400 ppm | Frontal headache, nausea | 1-2 hours; dangerous within 3 hours | | 800 ppm | Dizziness, convulsions | 45 minutes; fatal within 2-3 hours | | 1,600 ppm | Headache, dizziness, nausea | 20 minutes; fatal within 1 hour | | 3,200 ppm | Headache, dizziness, nausea | 5-10 minutes; fatal within 25-30 minutes | | 6,400 ppm+ | Convulsions | 1-2 minutes; fatal within 10-15 minutes |
Source: CDC/NIOSH CO exposure limits
Why CO is dangerous when sleeping: Symptoms at lower concentrations feel like a headache or flu. People fall asleep with mild symptoms and don't wake as CO concentrations increase. This is why CO kills sleeping people — the escape response fails. A detector must alert before symptoms reach incapacitation.
CO Detectors: What You Need
Minimum standard: One detector on each floor of the home, including the basement. One within 15 feet of each bedroom.
Types:
- Plug-in with battery backup: Most reliable for permanent installation. Plugs into wall outlet, battery backup for power outages. Critical: these continue working during outages.
- Battery-only: For areas without convenient outlets and for portability. Replace batteries annually.
- Combination smoke/CO detector: Acceptable, but some building codes require separate dedicated detectors for reliability verification.
What a detector measures: CO concentration in ppm over time. Different alarm thresholds exist — most residential detectors alarm at 70 ppm sustained (to avoid nuisance alarms from brief cooking), which is appropriate for normal conditions. Higher sensitivity (35 ppm) is appropriate for sleeping areas.
Lifespan: Most CO detectors have a 5-7 year sensor life. Check the manufacture date on the detector. An expired sensor may not detect CO at all. Replace when the detector signals end-of-life or at 7 years.
For emergency scenarios: Have a battery-operated or combination CO detector to function during power outages. A detector that requires wall power offers no protection exactly when you're most likely to need it.
Generator Safety
Generators are involved in a disproportionate number of CO deaths — they produce large quantities of CO and are often used during power outages when people are improvising.
Non-negotiable rules:
- Never run a generator inside the home, garage, basement, or any enclosed or partially enclosed space
- Minimum 20 feet from windows, doors, and vents — CO exhaust must be directed away from the structure
- Never run a generator under an overhang or carport where exhaust can accumulate
- Never run in a garage even with the door open — CO concentrations build faster than people expect
If someone is found unconscious near a generator: Assume CO poisoning. Drag or carry them to fresh air immediately — don't wait for help. Call 911. CPR if not breathing.
Emergency Response to CO Alarm
- Get everyone out immediately — don't stop for anything
- Leave doors open as you exit (ventilates the structure)
- Call 911 from outside
- Don't re-enter until responders clear the structure
- If anyone has symptoms (headache, dizziness, nausea, confusion), they need medical evaluation — high-flow oxygen treatment is most effective when given early
If symptoms but no alarm: Trust the symptoms. CO detectors alarm at sustained levels; brief high peaks can cause symptoms before the alarm triggers. Headache + dizziness + combustion source in use = get outside first, investigate second.
Prevention During Extended Outages
Extended power outages are when CO risk is highest. The correct hierarchy:
- Electric heating alternatives first: Battery-powered space heaters, extra blankets, thermal sleeping bags, gathering people into one small room to conserve body heat
- Properly vented combustion appliances second: A correctly installed wood stove or fireplace with a clean chimney and working flue is safe to use indoors
- Outdoor-only combustion for everything else: Generators, propane heaters, camp stoves — outside, always
A CO detector and a plan for what to do when it sounds are more valuable than any fuel source. Without the detector, you're operating blind.
Sources
Frequently Asked Questions
How quickly does carbon monoxide become dangerous?
At 200 ppm (parts per million), CO causes mild headache, fatigue, and dizziness within 2-3 hours. At 400 ppm, frontal headache within 1-2 hours, life-threatening within 3 hours. At 800 ppm, dizziness, nausea, and convulsions within 45 minutes, death within 2-3 hours. At 1,600 ppm, death possible within 1 hour. At 3,200 ppm, death within 25-30 minutes. A generator running indoors can produce 3,200+ ppm rapidly in a normal-sized room.
Where should carbon monoxide detectors be placed?
The CDC and NFPA recommend CO detectors on every level of the home, including the basement, and within 15 feet of every sleeping area. CO is roughly the same density as air (slightly lighter), so it distributes throughout a space rather than pooling at floor level like propane. Placement at breathing height (5 feet) or as per manufacturer instructions is appropriate. Do not place directly above combustion appliances or within 5 feet of cooking appliances (normal cooking can temporarily trigger alarms).
What do you do when a CO alarm sounds?
Immediately get everyone (including pets) outside to fresh air. Don't stop to gather belongings. Call 911 from outside. Don't re-enter the structure until emergency services have identified the CO source and declared it safe. At the hospital or with emergency responders, tell them you were exposed to CO — treatment with high-flow oxygen is most effective when given promptly. Symptoms may include headache, dizziness, nausea, or confusion, but high-concentration exposure can incapacitate before symptoms are recognized.